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May 2005 (Vol 26, No 5)

Toxicology Brief: Potentially Toxic Garden Plants

Spring is here and the air is heating up. As your clients head for their gardens, tools in hand, are you prepared for the calls that you may receive regarding ingestion of certain garden plants by pets? There are numerous facts and myths surrounding which plants can actually be harmful to small animals. Just remember when dealing with toxicology, any plant can be problematic if the animal ingests an inappropriate amount.

Potentially Hazardous Plants

Tomatoes

Tomatoes (Solanum lycopersicum) belong to the nightshade family.1 Ingestion of the greenery, flowers, and green fruit can cause clinical problems in dogs and cats. Tomatine, an alkaloid related to solanine, is the agent that is concentrated in the young fruit and plant. As the plant ripens, the tomatine is metabolized. Therefore, ripe tomatoes are less likely to be problematic for animals. Clinical signs include gastrointestinal (GI) upset, cardiac effects, and central nervous system signs (e.g., ataxia, muscle weakness, tremors, seizures), resulting from cholinesterase inhibition. Because tomatine is very poorly absorbed orally, systemic effects are rare. As with all intoxications, the severity of clinical signs depends on the amount ingested. Treatment usually consists of symptomatic and supportive care.2

Grapes

Grapes (Vitis spp) are commonly grown in backyards where dogs are frequently exercised. Recently, the ASPCA Animal Poison Control Center has identified cases of acute renal failure associated with ingestion of grapes and raisins by dogs.a It is unknown by what mechanism renal failure develops. The syndrome may affect only a certain population of dogs, but no relationship has been found between breed, age, or sex. It is unknown if similar signs occur in cats. With acute exposure, renal damage may occur within 24 hours, causing azotemia. Other clinical signs in dogs are vomiting, diarrhea, anorexia, and oliguria. The treatment for grape toxicosis is fluid diuresis to protect the kidneys and maintain adequate urine output. Renal values should be monitored closely. Prevention is the key. Let your clients know that this fruit can cause life-threatening clinical problems and that grapes should not be fed as treats.2

Avocado

The avocado (Persea americana) is a common food that seems perfectly harmless. However, avocados have been shown to cause mammary necrosis in goats within a few hours of exposure.2 Avocados are also believed to cause myocardial degeneration in cattle, mice, rabbits, fish, and birds. Birds that ingest even the smallest amount should be decontaminated promptly to reduce the possibility of fatal signs. The effects on dogs and cats are not completely understood. GI signs are commonly seen and should be treated symptomatically. In addition, the animal should be monitored closely for other clinical signs related to the cardiovascular system.1,2

Rhubarb

Rhubarb (Rheum rhabarbarum) is another common plant that your clients may have in their gardens. This plant contains oxalic acid, which can cause damage to the GI tract and the kidneys in dogs and cats. The leaves of the plant can cause vomiting, diarrhea, and oral irritation. Oxalic acid can lead to the formation of calcium oxalate crystals, which cause renal tubular damage resulting in renal failure. The treatment for this type of ingestion is symptomatic and supportive care for the GI tract and fluid diuresis to help protect the kidneys.2

Onion and Garlic

Onion (Allium cepa) and garlic (Allium sativum) are in the same family and can affect animals the same way. All types of onions and garlic can cause clinical problems. Allium spp can cause Heinz body formation, methemoglobinemia, agglutination, and hemoglobinuria. Cats are more sensitive to Allium toxicosis than dogs. In addition to anemia, small animals may exhibit GI signs, including anorexia, vomiting, and diarrhea. The anorexia often occurs 1 day before the hemolysis. GI signs should be managed, and the patient's hematocrit level should be monitored closely. A blood smear should be conducted to determine the presence of Heinz bodies.1-3

Common Nontoxic Food Plants

Many garden foods are not expected to cause life-threatening signs. Keep in mind that any time an animal ingests anything that it is not accustomed to eating, mild to moderate GI signs may result. Different types of squash, such as acorn, buttercup, and butterfly, fit into this category. Zucchini, cucumbers, melons, and bananas are also nontoxic to pets.

When outside, pets also have access to seeds that have fallen to the ground. Apple and cherry seeds are often thought to be poisonous. Although they do contain cyanide, the amount is very small. In addition, the seeds usually are not broken open when ingested. There is a higher probability that the seeds will cause a foreign body obstruction than toxicosis from cyanide.4